Does this Ring outside door sensor need a base station to work?

No. It connects over Amazon Sidewalk and does not require a base station, though Amazon Sidewalk is required for use and coverage may vary.

Can this outside door sensor be used to monitor outdoor areas like gates, sheds, garages, and storage spaces?

Yes. It is designed to secure outdoor access points and can monitor gates, sheds, garages, and storage spaces.

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Ring Outside Door Sensor - Weatherproof Entry Alert, Amazon Sidewalk, No Hub Required, Up to 10-Year Battery Life

WEATHERPROOF OUTDOOR ENTRY DETECTION: Rated IP66 for dust and water resistance, this sensor monitors gates, sheds, and other outdoor entry points that indoor-only sensors can't cover, sending an alert the instant it opens.
NO HUB OR WIFI RANGE LIMITS: Connects automatically over Amazon Sidewalk, a free nationwide network covering approximately 95% of the US population, so there's no base station to buy and no dependence on your home WiFi's outdoor reach.
UP TO 10 YEARS OF BATTERY LIFE: Powered by 2 included AA alkaline batteries rated for up to 10 years of use (varies by event frequency and proximity to a Sidewalk Gateway), so it keeps watch with minimal upkeep.
OPTIONAL 24/7 PROFESSIONAL MONITORING: With a compatible Ring subscription (not included), add professional emergency dispatch, remote arm and disarm from the Ring app, and SOS emergency response on top of real-time notifications.
COMPACT, NO-SUBSCRIPTION MONITORING: Works with Alexa and mounts easily with the included screws, anchors, and screwdriver, with no hubs, sign-up fees, or subscriptions required just to connect.